The engine P1691 Code can describe the problem of the car engine. You should fix the car engine according to the description if you know. Otherwise, the problem of the car engine will be fixed by an automobile engineer. The expert engineer knows well how to check the car engine and how to fix the car engine issue. So, you have to take the car to a right place where you will get support from the expert automobile engineer. Do not drive the car with the engine problem. The problem can be worse and very serious later what may be more expensive to solve.